Titanium and titanium alloys are frequently used as implant materials in dental and orthopedic surgery because of their good compatibility with bone tissue and thir tendency to form a firm attachment directly with bone tissue. The interaction between bone tissue and metal, leading to such firm attachment, was coined "osseointegration" by Brinemark and co-workers, of Gothenburg, Sweden, in the late 1970's, but the mechanics of the attachment process are not yet fully understood.
The standard surgical technique for fixing a surgical implant involves a two-stage process. In the first stage the soft tissue covering the bone tissue is opened and a base pan of the implant is placed in the bone tissue. The soft tissue is closed and the implant left to osseointegrate for a comparatively long period of time. In the second stage the soft tissue is re-opened and the load-bearing parts of the implant are attached to the base part A two-stage technique such as this has some disadvantages, since the long period needed for osseointegration is very uncomfortable for the patient Furthermore, in orthopaedics it is preferable to have a one-stage operation since a joint, for example the hip joint, should not be operated on twice if this can be avoided. One prerequisite of a one-stage operation is that the time needed to obtain sufficient strength at the bone tissue -implant interface, is short. In addition, there may be problems in obtaining a full osseointegration in those cases where the quality of the bone is poor or the available space is limited, for example in the upper jaw or in the posterior parts of the lower jaw above the nerve. In these places it would therefore be desirable to stimulate the regeneration of the bone tissue around the implant.
There are to date several methods for treating implants made of titanium in order to obtain a better attachment of the implant. Some of these involve altering the topography of the implant, for example by creating relatively large irregularities on the implant surface in order to obtain a better mechanical retention and to increase the area of attachment, by for example plasma spraying, blasting or etching. Although the retention may be improved, the time necessary for the osseointegration process may be longer since the bone tissue would have to grow into the irregularities in the surface.
Other methods involve altering of the chemical properties of the implant surface. For example one such method involves the application of a layer of ceramic material such as hydroxyapatite to the implant surface, inter alia in order to stimulate the regeneration of the bone tissue. Ceramic coatings however may be brittle and may flake or break off from the implant surface, which may in turn lead to the ultimate failure of the implant.
U.S. Pat. No. 4,330,891 could perhaps be said to combine each of the above, in that the provision of an element with a micro-pitted surface which micro-pits are within a certain diameter range, is said to effect improved properties as regards acceptance of the carrier element, and primarily improved durability of the healthy ingrowth of the element due to its biological quality.